1. Field of the Invention
The present invention relates to a method of manufacturing hexagonal ferrite magnetic particles and to the hexagonal ferrite magnetic particles obtained by the above method. More particularly, the present invention relates to a method of manufacturing hexagonal ferrite magnetic particles making it possible to provide microparticles by inhibiting the aggregation of particles in a step of fertilization by calcination, and to the hexagonal ferrite magnetic particles obtained by the above method.
The present invention further relates to usage of the above manufacturing method and hexagonal ferrite magnetic particles.
2. Discussion of the Background
Hexagonal ferrite is employed in permanent magnets. In addition, it has also been employed as a magnetic material in magnetic recording media in recent years.
The method (coprecipitation method) of fertilization by conducting calcination of a coprecipitate obtained by coprecipitating an iron salt and an alkaline earth metal salt is a known method of manufacturing hexagonal ferrite (see Japanese Unexamined Patent Publications (KOKAI) Heisei No. 7-172839 and No. 2010-1171, which are expressly incorporated herein by reference in their entirety). The method of obtaining a coprecipitate by forming a reverse micelle (reverse micelle method) has been proposed as an improved coprecipitation method (see Japanese Unexamined Patent Publication (KOKAI) No. 2007-91517, which is expressly incorporated herein by reference in its entirety). The application of the reverse micelle method to the manufacturing of ∈-iron oxide, employed as an electromagnetic wave absorber, is proposed in Japanese Unexamined Patent Publication (KOKAI) No. 2008-277726 or English language family member US2010/238063A1 and U.S. Pat. No. 8,072,365, which are expressly incorporated herein by reference in their entirety.
US2003/0077382A1, which is expressly incorporated herein by reference in its entirety, describes that spherical ferrite particles can be obtained by adhering barium or strontium carbonate to iron oxide or iron hydroxide and then conducting calcination.
As the volume of information being recorded has grown, ever higher density recording on magnetic recording media has been demanded. Reducing the size of magnetic material is necessary to achieve higher recording densities. In the coprecipitation and reverse micelle methods, there is a problem in that the particles sinter and aggregate during calcination, making it difficult to achieve minute particles.
The method described in US2003/0077382A1 presents this same problem because calcination is conducted to produce ferrite.
With regard to the above, Japanese Unexamined Patent Publication (KOKAI) No. 2007-91517 proposes that sintering be inhibited by coating the coprecipitate with an alkaline earth metal compound before calcination. However, based on investigation by the present inventors, the anti-sintering effect achieved with an alkaline earth metal compound is not necessarily adequate. Achieving higher density recording requires more effective means for preventing sintering.